The method of improving the display brightness of the display device by improving the brightness of a single light source and/or increasing the number of light sources will result in the increased heat output of the light source or the light sources. If the heat cannot be dissipated out in time, the temperature of the light source(s) and areas near the light source(s) will be raised, so that the service life of the light source(s) can be affected, and other adjacent optical components can be deformed. For instance, in a display device which takes light-emitting diodes (LEDs) as light sources, when the brightness of the LEDs is higher than lumen (Lm), after the LEDs are lightened at a rated current and operate for a period of time, local temperature around the LEDs will be gradually raised and exceed 55° C. Once the temperature of the LEDs is higher than 55° C., a light guide plate (LGP) and a reflector plate making tight contact with the LEDs may produce irreversible bending deformation due to high temperature. In addition, if the number of the LEDs in a light bar is larger, the accumulated heat energy is larger, and hence the possibility of adverse effects is higher.